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COMPOSITE STRUCTURES IN AN AMORPHOUS STATE FOR PHOTOCATALYSIS
The present invention relates to a new type of
photocatalyser - composite structures in an amorphous state -
which operates based on the phenomenon of the forced separation
of free charge carriers (electrons, holes) preventing their
immediate recombination.
Existing principles and techniques
The photocatalytic effect is based on the
phenomenon of the stimulation of a semi-conductor by Light
rays (UV or Visible) . The photonic stimulation causes the
generation of "electron — positive hole" pairs which result from
the passage of electrons from the valence band of the semi
conductor to its conduction band. Because of the presence of
forbidden zones which perform the role of energy barriers
against the recombination of free charge carriers, these being
able to access the surface of the solid body, attacking the
absorption complexes and therefore promoting their
transformation into end products.
Currently, only semi-conductors (solid crystalline
body) in the form of micro- and nanoparticl.es are considered to
be promising photocatalysers. Their crystallinity guarantees,
on one hand, an effective separation of the charge carriers
(e~, h+) and avoids their immediate recombination. On the
other hand, the sizes of these crystallite particles are
proportioned, preferably, in tens or hundreds of
nanometres, in order to ensure that a great number of the
free carriers have access to the contact surfaces. These
proportions are compatible with the distances covered by
the free charge carriers in a crystalline body during their
average lifetime, as mentioned in reference [1] of: the
bibliography.
In that which follows, the numbers in square
brackets correspond with the bibliographic references at
the end of the present description.

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Figure 1 presents 3 principal types of active
materials known to demonstrate important photocatalytic
capacities. These materials include photooataiytjc
components generally in the crystallite state.
The most widely used industrial photocataiyser is
the product being sold by Degussa - Deutsche Gesel l.scha f t,
Germany (commercial name: Degussa P25, crystallite product
in titanium dioxide containing ~ 80% of the anatase phase
and ~ 20% of the rutile phase) [2].
Currently the processing of crystal Litie
nanoparticles of titanium dioxide is carried out, in most;
cases, using techniques based on the application of: plasma
or by the Sol-gel process. The plasma techniques [cf. 3,
for example] using the precursors of titanium, organic or
inorganic, in a gaseous state which ionise at high
temperatures. In the presence of oxygen, the ions Ti4+gas
transform into titanium dioxide TiO2 clustered in nanopart.ic.1es.
The Sol-gel process is based on the hydrolysis of the sols
of alkoxides of metals of which the end products are metal
oxides. The nanoparticles of TiO2 can be processed,
respectively, by the hydrolysis of titanium alkoxides under
controlled conditions [4].
More sophisticated processes, such as Layer-by-Layer
Self-Assembly (LBL-SA) [5] or ultrasonic Spray Pyrolysis (USP)
[6], are also applied, at laboratory scale, for the fabrication
of nanometric crystals.
The techniques described in [5, 6] also permit the
obtention of crystallite particles of an optimal size (10 - 100
nm in diameter). These dimensions are considered to be the most
appropriate for photocatalytic application.
However, the products produced by the processes in
references [3-6] always represent "prefabricated" substances
which afterwards need a solid fixation on the medium wa 11 s in
order to be applied as elements of photocatalytic units. The
only mechanism which permits the fixing of an existing

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crystallite particle ("prefabricated") to an external medium .is
its physical adhesion. Physical adhesion, on the other hand,
does not permit the successful creation of composites which are
sufficiently stable. Mechanically very fragile, these systems
rapidly degrade during use.
In order to avoid these difficulties relating to the
manipulation of prefabricated crystallite nanoparticles, it is
sensible to envisage replacing them with composite products
which can have an active phase chemically grafted in situ onto a
medium.
Current scientific documentation presents a certain
number of expensive and sophisticated techniques for the
processing of composite products with photocatalytic properties
(examples: Arc Ion Plating (AIL3) [7], Dip-coating [8|, Photo-
Inducted Sol-gel [9], Plasma Associated Metallo-Organic CVI) [10,
11], Sputtering [12, 13], Photo-assisted pulsed laser deposition
[14], etc.).
Currently, these processes do not exceed laboratory
scale. On the other hand, their application ai 1ows the
processing of composite structures containing Ti.O2 crystallite
nanoparticles grafted onto various porous supports (SiO2, y-A]?O3/
active carbon, etc.). In general, these products demonstrate a
photocatalytic activity comparable to that of the Degussa p2b.
The techniques [7-12, 14] and other modern techniques
are required for the processing of composite photocata1ysers
which have active phases presented by crystallite
nanostructures. In cases where the active components are
initially formed as disorganised structures, they undergo
complimentary treatments, such as irradiation or calcination, in
order to transform them into a crystallite state, as described
in [11].
Apart from some rare references (for example [13, 15,
16]), non crystallite materials are not considered to be
photocatalytic products because of their disorganised structures
which favour an immediate recombination of charge carriers. In

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effect, the absence in the disorganised structures of .internal
energy barriers (forbidden zones) reacting against the immediate
recombination of charge carriers is considered to be a fatal
obstacle preventing the amorphous products from competing with
the crystallite products.
The invention
The invention relates to a composition and an
operating principle of a composite photocatalyser having an
active phase which constitutes nano- and micrometric spherical
aggregates of titanium dioxide in an amorphous state, chemically
linked with the surface of a medium which demonstrates strong
acidic or Lewis base properties and therefore performing, during
the active phase, the role of the source of an external electric
field causing the forced separation of free charge carriers by
neutralisation (trapping) of charges of a first type(negative or
positive) in favour of another.
More particularly, the invention is the result of the
hypothesis that it is possible to make amorphous structures work
as heterogeneous photocatalysers by separating the charge
carriers using an external force. The role of this external
force can be performed by the interactive energy between
opposing electrical charges. For example, carriers of a first
type, negative or positive, can be selectively neutralised in
situ by a medium demonstrating particular types of electrical
properties - acceptor or donor properties. In this favourable
situation the carriers of a second type are protected against
immediate recombination.
Thus the invention refers to composite structures in
an amorphous state which operate according to the phenomenon of
forced separation of free charge carriers (electrons, holes)
preventing their immediate recombination.
Acceptor mediums which have important levels of Lewis
acidity, such as silica, aluminium oxide, aluminium phosphate or
zirconium oxide are the only ones which are used when combined

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as electron traps, whilst metal mediums demonstrating strong
Lewis base properties are used as hole traps.
Thus, the invention relates, generally, to a composite
system comprising a photocatalytic component i.n an amorphous
state and an active medium intended to neutralise the free
charge carriers of a first type, electrons or positive "holes",
in order to protect the charge carriers of a second type against.
recombination.
In one embodiment, the active medium is an acceptor
medium high in Lewis acidity.
Alternatively, the active medium is a donor medium.
According to one embodiment, the photoeatalytic
element (active component) is made of disorganised (amorphous)
nano- and microparticles of titanium dioxide chemically .Linked
to a medium in order to ensure an effective transfer of
neutralising carriers towards the mass of the acceptor or donor
medium.
The invention thus concerns, in one embodiment, the
use of titanium dioxide as an active component of: the
photocatalytic processes. It substitutes the crystallite
structures currently used in the practice, with composite
products consisting of amorphous nanoaggregates of T.102
chemically fixed to the surfaces of solid mediums having
important electron accepting or donating capacities
(acceptor/donor mediums).
The photocatalytic activity of amorphous TiO2 is due
to the artificial separation of charge carriers (e-, h-t) in the
external electric field supplied by the acceptor/donor medium.
This forced separation protects the charge carriers from
immediate recombination and permits the carriers of a selected
type to retain their free states when travelling towards the
active surfaces. Carriers of a second type are neutralised in
situ by the activity of the medium.
For the methods of the invention, an example is
described which concerns the processing of composite

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products of type "amorphous nanoaggregat.es TiO2 - oxide
medium having pronounced acceptor capacities".
The surfaces of amorphous oxides have several
functioning groups. In ambient conditions and up to 250-300 °C
they are enriched in active Broensted sites (acid and base).
This active population permits the chemical grafting onto the
oxide surfaces of modifiers of various types.
The processing of TiO2 composite structures,
crystallite and amorphous, on mineral mediums can be carried out
by most of the methods mentioned below. From the technological
point of view, these composites can be processed notably by Sol -
Gel, Sputtering, Plasma Assistance CVD and ML-ALE-CVD, which
signifies Molecular Layering or, according to alternative
terminology, Atomic Layer Epitaxy [17], 18]. The latter, thanks
to its relative simplicity, appears to be the best adapted for
the processing of the proposed products, in particular of the
type "amorphous TiO2 nano- microaggregates - acceptor medium",
under both laboratory and industrial conditions.
According to the ML-ALE-CVD process, a solid medium of
which the surface has been pre-functionalised in order to enrich
it in active Broensted sites, treated in situ by a volatile
mineral precursor (for example, an oxy-halogen or halogen
product - MeL0MHalN, MeLHalN) or an organometalli c product (for
example, an alkoxide - MeL-0RN) , then hydrolysed, transforms into
composite material "nanometric oxide aggregate - medium"
(reactions (1) and (2), example with the halogen precursor):

A series of composite products of the type "amorphous
TiO2 nanoaggregate - acceptor medium" can be processed using the
ML-ALE-CVD method having special operative parameters.

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The protection of free charges from recombination in
situ by their forced separation can also be carried out: by the
active donor mediums which perform the role of enriching the
photocatalytic aggregates in electrons. In this case, the oxide
mediums of a high Lewis acidity (electron acceptors) can be
replaced by porous mediums containing elementary metal
aggregates distributed on their surfaces. These donor mediums
supply additional electrons to the photocatalytic components by
immobilising the positive charges (electronic holes). The
processing of composite products of the type "amorphous TiO2
nano- microaggregate - donor medium" can be carried out by one
of the techniques devised for the creation of oxide deposits on
metal surfaces, for example the Sol-Gel technique.
Figure 2 represents a system according to the
invention which includes an active component 10 in an amorphous
state, and an acceptor medium 12 high in Lewis aci.dj.ty or a
donor medium. In the case of an acceptor medium the electrons e~
14 travel towards the medium 12. In the case of a donor medium
the electrons of the medium travel (marked with dotted lines)
towards the holes h+ 16 of the component 10.
Detailed example of embodiment
The composite products according to the invention
contain amorphous TiO2 nanometric aggregates grafted onto silica
(SiO2) and to activated aluminium oxide (Y-A12O3) mediums, as
well as onto complex mediums (SiO2 * Fe3+, . SiO2 * Cr2O72~, SiO2 *
CrO42", Y-A12O3 * Fe3+, y-Al2O3 * Cr2O72"', y-Al2O3* CrO42) . The
addition of Fe3+ or Cr6+ to pure mediums was chosen in order to
better demonstrate the functioning mechanism of the composites
"amorphous TiO2 -, microaggregat.es - acceptor medium". However,
these additions are not indispensable for the improvement of the
photocatalytic properties of the composite products according to
the invention.
The oxides that were chosen - SiO2, y-A!2O3 - as active
mediums are strong Lewis acids (electron acceptors). They are
capable of immobilising the negative charges (electrons) [19,

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20] while leaving "free" the positive charges (electronic ho.'les)
in the surface structures stimulated by the light rays.
Electronic holes are considered to be strong oxidants which
favour the effective degradation of pre-absorbed products on the
surface [21].
In order to test the photocatalytic activity of: the
processed samples, two reactions of the total oxidation of
volatile organic compositions were chosen: The photocataJytic
incineration of trichloroethane vapour (C2H3CI3) and that of
toluene vapour (C7Hs) :
C2H3CI3 + 2O2 2CO2 + 3HC.1 (3)
C7H8 + 9O2 7CO2 + 4ll2O (4)
One of the products of the total oxidation of
trichloroethane is hydrochloric acid, HC1 (reaction (3) ) . Its
high solubility in water (700 volumes HC1 to 1 volume water in
standard conditions) permits the monitoring of the
photocatalytic performances of trichloroethane C2H3Cl3 by
measuring the pH evolution in a receptacle that has been
agitated downstream of the test installation. The second
technique used for monitoring the photocatalytic performances of
C2H3CI3 and of C7H8 .was the chromatographic technique
(chromatograph Hewlett-Packard 5890 series II, with an IIP 5972
detector (FID)).
The photocatalytic tests were carried out under-
laboratory conditions. The operating parameters are presented in
table 1. All composite samples tested contained on their
surfaces between 6 and 7% in the mass of TiO2 in an amorphous
state (product N°3-5 and 7-9 in table 2 below or crystallite
product N°2 in table 2).
Table 1: Operating conditions

Parameters Value

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By comparing the photocatalytic samples on the pure
silica and activated aluminium oxide mediums, it is
noticeable that there is an important level of activity for
the first and a low level of activity for the latter (table
2, samples 3 and 7).
This difference in photocatalytic activity can bo
explained by the particularities of the dynamic systems
"TiO2-SiO2 and TiO2-yAl2O3". In effect, the capacities o C
silicas as acceptor mediums greatly exceed those of
aluminium oxides, thanks to the presence on the surface of
silicas of very strong Lewis acid sites [19] .
The activities of the samples based on the Degussa
p25, both pure and on an acceptor medium, remain superior
to those of composite "amorphous TiO2 - pure aluminium
oxide" (samples 1, 2 and 7 in table 2), whereas the
composite "amorphous TiO2 - pure silica" (sample 3) greatly
exceeds the products based on the Degussa p25.
Table 2. Photocatalytic activity of products in the
reaction of the total oxidation of trichloroethane C2H3C13



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In an effort to improve the photocatalytic
performances of composite products, a series of samples were
processed on oxide mediums doped in electron traps (composed
from a base of transition metals) . The aim of this approach was
to create acceptor mediums with higher capacities. As doping
components, ferric oxides (Fe2O3) were used which presented
active sites in the form of cations Fe2+ and FeJ+. Anionic chrome
complexes (chromates and bichromates - CrO,,2", Cr2O72 ) were also
applied.
The processing of doping mediums was carried out by
initial saturation of the mediums (SiO2, y-Al2O3) with metallic
salt solutions, followed by their thermal conditioning and
treatment (conditioning - 24 h, ambient temperature; drying - 8
h, temperature 110 °C; calcination - 4 h, temperature 550 °C).
The data presented in table 2 shows an important;
improvement in the photocatalytic activity of the samples [yAl2O3
- Fe3+] * TiO2 and [yAl2O3 - Cr6+] * TiO2 (samples 8, 9) in
comparison to the sample yAl2O3 * TiO2 (sample 7) . This phenomenon
could be explained by the presence of, on the surfaces of the

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doped aluminium oxides (yAl2O3 * Mex0Y) , stronger acceptor sites
than the initial sites (Al3+) [20] . By comparison to the pure
aluminium oxides, these medium complexes should therefore be
considered as more effective acceptor agents in the forced
separation of electrical charges.
On the contrary, the accepting capacities of electrons
for the mediums [SiO2- Fe3+] and [SiO2 - Crs+] were considered
lower compared to those of pure silica: The photocatalytic
activities of samples 4 and 5 remain lower than the activity of
sample 3 (table 2) . These circumstances are due, very probably,
to an exceptional number of sites Si4+ such as Lewis acids [19].
It should be noted that the influence of the mediums
of origin (SiO2 and y-Al2O3) on the effectiveness of the charge
separation rapidly diminishes when they are enriched in doping
components. For example, samples 5 and 9 (table 2) demonstrate
the same photocatalytic activities, even when sample 5 is
processed on a medium of SiO2 and sample 9 on a medium of y-
A12O3.
The best results are obtained when using the acceptor
medium of pure silica (sample 3 in table 2) . This fact
demonstrates that it is not necessary to supply additional
acceptors (electron traps) in the composite products of type
"amorphous TiO2 nano- microaggregates - acceptor medium" where
the medium is composed of silicas.
Figure 3 represents the temporal evolution of the
concentration of toluene downstream of the photocatalytic unit.
Curves 22-24 comprising empty triangles, squares and diamonds
correspond respectively with the Degussa p25 curves without
light, of the composite "silica - TiO2" without light and of the
composite "aluminium oxide - TiO2" without light. Whilst curves
25-27 comprising filled triangles, squares and diamonds
correspond respectively with the Degussa P25 curves with light,
of the composite "silica - TiO2" with light and of the composite
"aluminium oxide - TiO2" with light.

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Table 3 below represents the photocatalytic activity
of products in the reaction of the total oxidation of toluene
C7H8:

The behaviour of the samples in respect of the
photocatalytic treatment of air carrying toluene vapour
represented throughout this table 3 and this figure 3 can be
discussed in terms of the absorption capacities of porous
composites and in terms of the electronic properties of the
active mediums.
The best photocatalytic capacities are always
manifested by the composites "amorphous TiO2 nano-,
microaggregates - acceptor medium" of a silica base (sample 1 in
table 3 and curve represented by full squares on figure 3) . On
the contrary, the composite sample of a cardboard base (No 4 in
table 3) does not possess any activity because its medium does
not have electron acceptor capacities and therefore cannot
activate the amorphous TiO2 aggregates on its surface.
In the case of toluene C7H8 on which the solid surface
absorption facilities are greatly superior in comparison with
those of trichloroethane C2H3C13, the sample of an activated
aluminium oxide with the specific surrounding surface of 260-270
m2/g having a photocatalytic activity superior to that of the
Degussa p25 which has a specific surface of less than 50m2/g.

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In the case of toluene and in that of trichloroethane,
the photocatalytic activities are therefore reversed (cf. table
2 and 3). This phenomenon can be explained by the fact that the
porous mediums, which have high absorption capacities, like
silicas and activated aluminium oxides, can contribute to the
photocatalytic performance of pre-absorbed products by
transforming, at high speed, their absorbing complexes into end
products. This hypothesis is verified by the comparative
analysis of test results presented in the columns "absorption
capacity without light" and "photocatalytic activity" in table
3, as well as by the comparison of curve appearance obtained
with and without light in figure 3.
In addition, figure 4 shows the curves representing
the state of crystallinity in samples using the XRD (X-Ray
Diffraction) technique. These curves were obtained during
analysis carried out by M. Pierre Gaudon from the Ales School of
Mines.
This figure 4 demonstrates that the composite
structures according to the invention are amorphous. In effect,
curves 30 and 31 of products according to the invention based on
aluminium oxide and silica possess values of a state of
crystallinity largely inferior to those of the Degussa p25
represented by 29.
Figure 5 shows images of the surface structure of
mediums and of composite products according to the invention.
These images were obtained using an MEB (Sweep Electronic
Microscope) by Paul Jouffrey of the Saint-Etienne School of
Mines.
More precisely, figure 5a shows a surface of a medium
32 in aluminium oxide. And figure 5b shows aggregates 33-35 of
TiO2 on the medium 32 in aluminium oxide.
In addition, figure 5c shows a surface of a medium 36
in Silica. And figure 5d shows aggregates 37-39 of TiO2 on the
medium 36 in Silica.

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These aggregates are spherical and have an average
diameter of between 500 and 2000nm.
The advantages of new active products (photocatalytic
activity, method of production, application):
The photocatalytic activity of amorphous composites
"TiO2 - porous acceptor medium (donor)" greatly exceeds those of
the Degussa p25 (commercial photocatalyser, cf. table 2, samples
1 and 2).
Compared to pre-fabricated crystallite structures,
the composites "amorphous TiO2 nano-, microaggregates
porous medium" are equally advantageous from a
technological point of view (their simplicity of
fabrication as an active element ready to be used and their
fixing reliability onto the surfaces of mediums).
Their eventual application can therefore be very
favourable in the processing of photocatalytic elements
(reactor sections, active panels etc.) under industrial
conditions.
It will be noted that the amorphous photocatalytic
composites "TiO2 - donor medium" can be difficult to achieve in
cases where the existing mediums are in the form of factory
parts (tubes, plates, panels etc.) This drawback, is caused by
the non porous nature of metals.
Variations and Extensions of the invention
Research has been carried out in order to demonstrate
the sterilising capacities of composite products according to
the invention.
Figures 6 additionally show an experimental device for
testing sterilisation capacities. The genetically modified
Escherichia coli bacterium (source - INRA, France) was chosen as
the bacterial species for testing.
In a first stage represented on figure 6a, the
photocatalytic composite samples 43 and the non-modified mediums
44 were soaked with a bacterial mist 45 during 3 minutes.

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This mist 45 was obtained from dry air 47 and a
bacterial solution 46 placed at an end 48.1 of a tube 48. This
dry air 47 blown from the end 48.1 across the solution 46 in
such a way as to create a bacterial mist 45. The mist 45
therefore circulates in the tube 48 and soaks the samples 4 3 and
44 which are at an end 48.2 of the tube 48 opposite to 4 8.1.
In a second stage represented by figure 6b, a sample
of photocatalytic composites 43.1 was exposed to irradiation UV-
A (wave length 365nm) under an UV lamp 49. And a sample 43.1 of
a composite according to the invention was exposed to sunlight.
In addition, a non-modified medium 44.1 was exposed to sunlight.
All of these exposures lasted 20 minutes.
In a third stage represented by figure 6c, the samples
43.1, 43.2 and 44.1, or their surfaces were transferred into two
Petri dishes 50 containing a nutritive gel 51. These dishes were
left in the dark during 20 hours at 35°C in order to promote the
development of bacterial colonies. A part 52 of each dish 50
does not contain any of the sample and serves as a reference for
the experiment.
Figure 7 represents the development of bacterial
colonies in the Petri dishes, after conservation, for each of
the aforesaid samples. These tests were carried out in
cooperation with Christine Blachere-Lopez, of the Ales School of
Mines.
In sectors 4 and 12 containing only the nutritive gel
and serving as a reference sector, no bacterial colony
developed.
In sectors 1 and 9 the dishes containing samples 44.1
of pure silica (non-modified medium) exposed to sunlight,
respectively 21 and 6 bacterial colonies referenced 53 developed
within 20 hours of incubation.
In sectors 3 and 11 containing samples 43.2 of a
composite according to the invention exposed to sunlight, only
one bacterial colony 53 developed.

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In sectors 2 and 10 containing samples 43.1 of a
composite according to the invention exposed to UV--A
irradiation, no bacterial colonies developed.
In other words, 27 colonies (21+6) developed on the
surfaces of the non-sterilised samples 44.1 against only one on
the surfaces of samples 43.1 and 43.2 of the product according
to the invention.
This data shows that the amorphous TiO2 composite
structures according to the invention demonstrated an important
capacity for sterilisation both under artificial irradiation (UV
"black light",λ, = 365 nm) and under sunlight.
These active products can therefore be conceived for
the photocatalytic reduction of volatile organic compositions of
a very large range, on condition that their initial
concentration does not exceed certain limits (for example, for
the gaseous phase - 3-H5 ppm; this case corresponds to the
conditioning of gas in confined spaces).
But these products can also be conceived as active
products in the collective and individual protection from
biological contamination.
An other area of application for amorphous composite
photocatalysers according to the invention can be the treatment
of waste liquids. Preliminary research was carried out to
demonstrate the advantages of applying these proposed products
in the photocatalytic purification of contaminated water by
organic composites in solution.
Thus, figure 8 shows graphic representations of a
photocatalytic degradation of acetone and ethanol in a liquid
phase using active composites of an amorphous TiO2 base under
sunlight.
A curve 55 consisting of triangles represents the
degradation yield of acetone, whereas as a curve 56 consisting
of squares represents the degradation yield of ethanol.
To obtain these curves 55 and 56, two liquid samples
of 25mL in volume containing 25mg/L of acetone and ethanol in

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water were brought into contact with two samples of composites
S-1T-070504 (sample N° 3 in table 2) where their masses were of
l.lg. Two identical liquid samples were brought into contact
with two samples of l.lg of pure silica. Four Petri dishes were
used as receptacles.
The mixtures were exposed to sunlight, under static
conditions during 2 days.
The losses of acetone and ethanol during their
photocatalytic degradation, taking into account the losses due
to evaporation were monitored using the chromatographic method.
The degradation yields of organic products in solution
were calculated by the differences between their remaining
concentrations in the receptacles containing pure silica (CSl02)
and their concentrations in the receptacles with photocatalytic
composites (Cphoto) , in comparison to the values of Csi02.
The first readings were taken in a dark room, before
the direct exposure of the samples to sunlight. Thus the points
of lOOhOO and of llh00 of the first day of the tests present a
negligible yield.
Next, the glass covered receptacles were taken out of
the dark room onto a sunny terrace. On the yield curves 55 and
56, two peaks 57 and 58 correspond to the maximum sunlight hour
(14h-16h). In a two day trial, the acetone and ethanol solutions
in the receptacles containing the photocatalytic samples were
completed degraded.
The variations and extensions of the invention can
therefore be envisaged, at least in the field of water
treatment, particularly for its purification and its
sterilisation; thereby in the field of the collective and
individual protection against biological contamination with, for
example, the implementation of air conditioning devices in
hospital sites, the creation of clothing and auto-sterilisation
tools...

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These photocatalytic materials according to the
invention can be implemented on various mediums (porous
ceramics, glass, cardboard paper, textiles etc.).

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15441 EN
-21-
CLAIMS
1 - Use of an acid or base medium for the forced
separation of free charge carriers generated by a photocatalytic
component in an amorphous state chemically fixed onto the said
active medium, by the immobilisation, in the said, medium, of a
first type of carriers, electrons or positive holes of the
photocatalytic component, in favour of another.
2 - A Composite system characterized in that it
comprises:

- a photocatalytic component in an amorphous state
chemically linked to an active medium, this photocatalytic
component generating free charge carriers, electrons and
positive holes when stimulated by light,
- the active medium being an acceptor medium in a
solid state having Lewis acid sites (cations), or a donor medium
in a solid state having free electrons, the acceptor medium
manifesting Lewis acid properties, the donor medium manifesting
Lewis base properties in such that

- where the active medium is an electron acceptor, the
electrons of the photocatalytic component stimulated by the
light are attracted by the acid sites of the active medium, and
- where the active medium is an electron donor, the
positive holes of the photocatalytic component stimulated by the
light are decimated by the free electrons of the active medium.
3 - A system according to claim 2, characterized in
that:
- the photocatalytic component is titanium dioxide.
4 - A system according to claim 2 or 3, characterized
in that:
- the photocatalytic component takes the form of nano-
or microaggregates.
5 - A system according to one of claims 2 to A,
characterized in that:

15441-EN -22-
- the active acceptor medium comprises components of:
strong Lewis acidity, such as silica, activated aluminium oxide,
aluminium phosphate, zirconium oxide, alone or combined.
6 - A system according to one of claims 2 to 5,
characterized in that:
- the active acceptor medium is doped with electron
traps of a transition metal base such as ferric oxide.
7 - A system according to one of claims 2 to 6,
characterized in that:
- the active electron donor medium comprises a metal.
8 - A system according to one of claims 2 to 7,
characterized in that:
- the active donor medium is doped by anionic chrome
complexes.
9 - A system according to one of claims 2 to 8,
characterized in that:
- the active medium operates as a source of external
electrical field for the forced separation of free charge
carriers and the immobilisation of a first type of carriers,
electrons or positive holes, in favour of another.
10 - A system according to one of claims 2 to 9,
characterized in that:
the active medium operating due to its own electronic
capacities consisting of donor or acceptor capacities, operates
the function of the role of the forbidden zone which can be
observed in the photocatalytic crystalline structures.
11 - Use of the system according to one of the
previous claims for the purification arid the chemical
conditioning of gas or of contaminated liquids and/or for the
sterilisation of these gases or contaminated liquids.

The invention relates to photocatalysis.
It concerns a composite system, comprising a
photocatalytic component (10) in an amorphous state and an
active medium (12) designed to neutralise the free charge
carriers of a first type, electrons or positive holes, in order
to protect the charge carriers of a second type from
recombination.